Master Circle of Willis with Picmonic for Medicine

The circle of Willis, named after an English physician, is a part of the cerebral circulation that is made up of the AComm (anterior communicating artery), ACA (anterior cerebral artery), ICA (internal carotid artery), which branches to the MCA (middle cerebral artery), PComm (posterior communicating artery), PCA (posterior cerebral artery), and basilar artery. The circle is a site of anastomosis between the blood supplied by the carotid arteries and the vertebral arteries to the brain. ACA is the anterior cerebral artery that makes up the front part of the circle of Willis. This artery supplies blood to the motor and sensory cortex that controls the lower limbs. Therefore, stroke due to the ACA would lead to contralateral paralysis and loss of sensation in the lower limbs.The anterior communicating artery is the artery in the circle of Willis that bridges the right and left anterior cerebral arteries. This is a common site for berry aneurysm, which can impinge on the cranial nerves leading to visual field defects.The internal carotid artery is a branch off of the common carotid artery and supplies many important structures in the head. There is one on each side of the neck and head. This artery is part of the circle of Willis and connects with the ACA and the posterior communicating artery. The internal carotid also branches off into the MCA. The middle cerebral artery is technically not considered part of the circle of Willis because it is an extension from the internal carotid artery. In fact, the internal carotid artery comes into the circle and leaves the circle as the MCA. The MCA supplies the motor and sensory cortex for the upper limb and face. Therefore, stroke in the MCA leads to contralateral paralysis and loss of sensation in the upper limb and face.Posterior communicating artery is the part of the circle of Willis that connects the internal carotid artery to the posterior cerebral artery. Like the AComm, this is a common site for berry aneurysm, which can cause CNIII palsy. CNIII palsy can lead to ptosis, pupil dilation, and the classic down and out eyes.The posterior cerebral artery bifurcates from the basilar artery and supplies the occipital or visual cortex. Stroke in this artery can lead to visual problems, specifically, contralateral hemianopia with macular sparing. Finally, the basilar artery comes from the confluences of the vertebral arteries and then bifurcates to become the posterior cerebral arteries. This can be considered as the most posterior aspect of the Circle of Willis. The basilar artery has multiple branches that supply the pons and medulla.